Stackable stamp



FIG. 1 is a front and top perspective view of a stackable stamp showing our new design, the side opposite being a mirror image;

FIG. 2 is a side elevation thereof, the side opposite being a mirror image

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is an end elevation thereof, the end opposite being a mirror image. 

The ornamental design for a stackable stamp, as shown and described. 